Storage,Quantity Characteristics And Ecology Effects Of Fallen Trees In Typical Forests Of Jiangxi

As an important part of the forests, the fallen trees are the foundation for species diversity in forest ecosystems, which also play a significant role in maintaining the species diversity, enhancing the soil fertility and accelerating the stand regeneration of forests. Is an important part of the forest ecosystem carbon stocks. Located in the subtropical regions of Jiangxi Province, the typical subtropical forests were selected for investigating the effects of forest types, stand types and disturbance on the biomass and carbon storage of fallen trees, and of the change of organic matter, nutrient contents in the decomposition of fallen trees on soil physicochemical properties. The results showed that:(1) There was significant effects of stand types on the biomass of coniferous forests(0.684 t/hm-2 in Chinese fir plantation and 0.553 t/hm2 in masson pine plantation) and evergreen broad-leaf forests(11.293t/hm2 in primary forests and 1.888 t/hm2 in secondary evergreen broad-leaf forests), but no significant differences of stand types on the biomass among mixed coniferous-broad-leaf forests(1.248 t/hm2 in mixed masson pine broad-leaf forests and 1.280 t/hm2 in mixed Chinese fir broad-leaf forests); and there was significant of stand types on carbon storage of in primary evergreen broad-leaf forests(4.781tc/hm2) and in secondary evergreen broad-leaf forests(0.812tc/hm2);the same to coniferous forests(0.279tc/hm2 in Chinese fir plantation and 0.207tc/hm2 in masson pine plantation) and mixed coniferous-broad-leaf forests(0.521tc/hm2 in mixed masson pine broad-leaf forests and 0.432tc/hm2 in mixed Chinese fir broad-leaf forests)(2) There was four diameter classes of the fallen trees in the coniferous forests, while only three diameter classes of that in the mixed coniferous broad-leaf forests; however, it indicated that five diameter classes of the fallen trees were uniformly distributed in evergreen broad-leaf forests; the density of different diameters of the fallen trees appeared to tend to 0-5 cm(Ⅰ)>5-10 cm(Ⅱ)>10-15 cm(Ⅲ); the biomass of the intermediately decomposed fallen trees were significantly higher than that of slightly and heavily decomposed one in evergreen broad-leaf forests and coniferous forests.(3) The biomass of fallen trees in artificial coniferous forest(0.825±0.20t/hm2) was significantly different from that of natural coniferous forest(1.647±0.19t/hm2), and greatly significant with that of natural evergreen broad-leaf forest(11.293±1.23t/hm2); the distributions of diameter class of fallen trees between plantations and natural forests were greatly different, and the diameter class of fallen trees in natural forests was distributed uniformly, with complex composition. The ratios of mildly decomposed fallen trees in plantations(61.9%) was significantly greater than that in natural forests(19.0%), while the ratios of intermediately decomposed fallen trees between them was reversal; there was significant difference among the mild, intermediate and severe decomposition of fallen tree biomass within natural forest. Because of differences in the storage, structure and decomposition of fallen trees, further researches are necessary for studying the impact of fallen trees on environment in the plantations and natural forests.(4) The lignin content was increasing gradually through the decomposition of fallen trees and the range of variation is 19.74~43.23%, while the cellulose content was decreasing along the decomposition, the range of variation is 9.97~37.97%. Compared with the slower decay of the lignin, the cellulose were suggested to be a more constant source of soil organic carbon, which provided more stable organic carbon for forest ecosystems. The carbon contents of broad-leaf(range of variation is 360.061~461.152g/kg) and coniferous trees(range of variation is 282.290~384.775g/kg)reduced gradually through the decomposition of fallen trees, with a significant effect of tree species, while the nitrogen contents increased along the decomposition. There was a significant effect of soil depth on the soil carbon contents in broad-leaf fallen trees, which was significantly differed from coniferous trees. Soil moisture content under fallen trees of coniferous species(23.58%) was higher than that of the broad-leaved species(20.4%), especially under severe decomposition 25.8% of fallen trees.